This invention relates generally to handwriting recognition, and more particularly to handwriting recognition in a pen-based computer system.
A pen-based computer system typically comprises a small, hand-held computer where the primary method for inputting data includes a "pen" or stylus which "writes" upon the screen of the computer system. The screen is a dual-function display assembly which serves as both an input device and an output device. When operating as an input device, the display assembly senses the position of the tip of a stylus on the viewing screen and provides this positional information to the computer's central processing unit (CPU). Some display assemblies can also sense the pressure of the stylus on the screen to provide further information to the CPU. When operating as an output device, the display assembly presents computer-generated images on the screen.
The dual-function display assemblies of pen-based computer systems permit users to operate the computer as a computerized notepad. For example, graphical images can be input into the pen-based computer by merely moving the stylus on the surface of the screen. As the CPU senses the position and movement of the stylus, it generates a corresponding image on the screen to create the illusion that the stylus is drawing the image directly upon the screen, i.e. that the stylus is "inking" an image on the screen. Besides serving as a notepad, pen-based computers can provide a number of useful functions, such as serving as an address book, an appointment calendar, a to-do list, etc.
Ink on the screen of a pen-based computer system is typically stored as a simple bit-map. Essentially, the only knowledge that the computer system has of the inked image is that certain pixels of the display are to be activated to create the inked image. Therefore a note, such as "Meet Bob Tuesday" has no meaning to the system other than certain pixels of the screen are to be turned on or off to create the inked image of the words.
It is often desirable to perform some level of recognition on the inked objects formed on the computer screen. In this way, additional meaning can be attached to the inked objects allowing the computer to manipulate the objects in a more intelligent fashion. For example, a common operation for pen-based computer systems is handwriting recognition. In this way, the inked object "Meet Bob Tuesday", can be "recognized" as comprising three words separated by spaces where each word comprises a number of letters. The recognized words and letters can be converted into an appealing font, and can be used and manipulated as words and letters rather than as bits in a bit-map.
There are a great many methods for recognizing handwriting known in the prior art. However, these recognition methods tend to be narrowly focused on a particular type of recognition task. For example, there are prior art recognizers for recognizing alphanumeric inputs, for recognizing graphical inputs, etc. If a recognizer of the prior art does not recognize a particular type of object that object is typically treated as ink.
Most handwriting recognizers require that a user enter handwritten information in a constrained manner. For example, many handwriting recognizers require that letters be entered in "block" form, rather than in a cursive fashion. Other word recognizers require that words be entered in particular fields or areas of the screen. Most handwriting recognizers require that words be written in a substantially horizontal manner from left to right.
These constraints limit the flexibility of handwriting recognizers, and takes some of the creativity and enjoyment out of the use of a pen computer system. It would be desirable to have a method and apparatus for recognizing handwritten words which would allow the characters of the word to be written in a free-form fashion at any angle, in any direction or order, and virtually anywhere on the screen of a pen computer system.